Ontology (from the Greek ὦν, genitive ὄντος: of being and -λογία: science, study, theory) is the philosophical study of the nature of being, existence or reality in general, as well as of the basic categories of being and their relations. Traditionally listed as a part of the major branch of philosophy known as metaphysics, ontology deals with questions concerning what entities exist or can be said to exist, and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and differences.

The principal questions of ontology are "What can be said to exist?" and "Into what categories, if any, can we sort existing things?" Various philosophers have provided different answers to this question.

One common approach is to divide the extant entities into groups called categories. Of course, such lists of categories differ widely from one another, and it is through the co-ordination of different categorial schemes that ontology relates to such fields as theology, library science and artificial intelligence.

Further examples of ontological questions include:

What is existence?

Is existence a property?

Which entities are fundamental?

How do the properties of an object relate to the object itself?

What features are the essential, as opposed to merely accidental, attributes of a given object?

What is a physical object?

Can one give an account of what it means to say that a physical object exists?

Can one give an account of what it means to say that a non-physical entity exists?

What constitutes the identity of an object?

When does an object go out of existence, as opposed to merely changing?

Why does anything exist rather than nothing?

MAKNA EPISTEMOLOGY

Epistemology (from Greek ἐπιστήμη - episteme-, "knowledge, science" + λόγος, "logos") or theory of knowledge is the branch of philosophy concerned with the nature and scope (limitations) of knowledge. It addresses the questions: